A conventional substrate strip for semiconductor packages is formed with plating buses and plating lines for plating a metal surface layer on contact pads. Normally the plating buses are extended to the sidewalls of the substrate strip. In the packaging processes, the substrate strip is conveyed by a track. The ESD (Electrostatic Discharge) will occur by the contact between the exposed plating buses at the sidewalls of the package substrate strip and the conveying track, which will damage the electrical functions of chips on the substrate strip. In order to prevent chips on the substrate strip from being damaged by ESD, R.O.C. Taiwan Pat. No. 508,769 discloses a conventional substrate strip with a layer of copper-mesh layer being electrically connected to the molding gate. While ESD is occurred during the molding process, electric charges are conducted to the copper-mesh layer and discharged. This will prevent a chip from being damaged by ESD during molding processes, but ESD still can happen while conveying the substrate strip.
Conventionally, to prevent ESD in a substrate strip is to route a through slot between units to remove plating buses on the scribe lines, and to cut off the plating buses extending to the edge of substrate strip and to create electrically “OPEN” between the substrate strip and the units. Nevertheless, the width of the through hole is larger than that of the scribe lines between the units, therefore, the effective area of the substrate strip for the units will be greatly reduced and the packaging cost will be increased, moreover, the package substrate strip is easily deformed.
Another conventional way to prevent ESD during conveying a substrate is revealed in R.O.C. Taiwan Pat. No. 479,344. At least a plating bus out of units and a plurality of branched plating lines inside the units are formed on a substrate. A plurality of bridging lines interconnect the solder-ball pads inside the units for plating. After electroplating, a plurality of holes are drilled in the bridging lines. The drilled holes are formed at the units and corresponding to each bridging lines in order to electrically isolate the solder-ball pads. Thereafter, an insulation material is filled in each drilled hole and even to the surface of the substrate. Nevertheless, the drilling holes are formed at the units, they may affect the package structure and reliability of the package substrates. To avoid this, they have to be filled with an insulation material, and this would increase packaging procedure and cost. Furthermore, the plating buses have to be redesigned to match up with the drilled holes.